It is known that the production of ceramic dental replacements may be done by means of a CAD (=computer-aided design) system which is part of a CIM (=computer-integrated manufacturing) system which is made available, for example, by 3M ESPE AG (Seefeld, Germany) under the name LAVA™. With this known LAVA™ system, the CAD system is on the one hand connected to an optical scanner and on the other hand to a NC-milling machine. The scanner captures the three-dimensional surface of a dentition impression and passes on the captured data to the CAD system. With the CAD system, the user can modify these surface data as desired, and calculate CNC data from said shape data using a CAM software, and then send the corresponding CNC data to the NC-milling machine. The NC-milling machine processes a zirconium oxide or zirconia ceramic blank in an as precise as possible agreement with the shape data. Finally, the milled ceramic blank is sintered.
During the sintering process, the ceramic material shrinks a certain amount. Typically, ceramic bridge frameworks are sintered on pegs made of alumina oxide or hangers made from a platinum alloy. Such pegs or hangers are placed on a honeycomb-like sintering tray in order to fit the framework geometry. This allows the framework to make any linear movement induced by said shrinkage. For example, anterior bridges are placed on one peg per coping at the exterior copings. Posterior bridges are placed on one hanger on the outer connector areas on either side. Such mounting technique is used for three- and four-unit bridges with two abutments as an outer unit and one or two pontics in between. This is described, for example, in WO 00/46166. In order to provide a support for the bridge framework during sintering, WO 00/46166 suggests supports that are not coated with metal and which adapt independently to the shrinkage dimensions which occur during the firing process. In more detail, WO 00/46166 describes as one example a support having at least two S-shaped hangers. The two S-shaped hangers are hung up on a horizontal bar. The bridge framework is mounted on the at least two S-shaped hangers. Such assembly provides for one swivel point for the article to be sintered. The two S-shaped hangers can swivel at the point where they are hung up on the horizontal bar. Thus, there is in effect one swivel point per hanger, and the swivel points of the two hangers are thus on the same horizontal axis.
In other systems, the ceramic framework is placed on ceramic balls or ceramic bulk material which is then placed in a container for sintering.